1. Field of the Invention
The embodiments described herein relate generally to differential signal amplifiers for use in transceiver circuits; and more particularly, to high voltage tolerant circuits for Current Mode Logic (CML) transceiver circuits that support different generations of interfaces.
2. Description of Related Art
Current mode logic (CML) transceivers are widely used in high speed digital applications. Some applications of CML circuits include serializer-deserializer (SerDes) circuits for high speed data transmission links. Typically under current trends, a situation is encountered where circuits having different specifications need to be coupled to one another. Furthermore, while current trends push towards circuits operating at lower supply voltages, there are still components in a system that may operate at higher supply voltages. It is often the case that an AC-coupled CML transceiver working with input signals having a supply voltage of 2.5 V (thus the signal itself being less than or equal to 2.5 V) may be connected to a circuit working with a 5V supply. Under current technologies, a first circuit working with a lower supply voltage specification may not be protected against signals coming from a second circuit having a higher supply voltage, generating a signal having voltage well above the specification of the first circuit, or “signal spikes.” In such an occurrence, the signal spike may over stress the components in the first circuit, leading to malfunction, signal distortion, and eventually catastrophic damage to the first circuit. Some of the components that may be affected in the first circuit are MOSFETs and diodes where the PN junctions may be driven beyond their breakdown voltage.
What is needed is a transceiver circuit that operates at lower supply voltage values and that may be immune to higher voltage signals coming from other circuits having a higher supply voltage.